Heat exchanger for refrigerator and method for manufacturing refrigerant tube of the same

ABSTRACT

A heat exchanger for a refrigerator is disclosed, which has a simple structure, an improved heat exchanging efficiency, and an operating reliability. In the heat exchanger including a refrigerant tube ( 10 ) having a plurality of straight parts ( 11 ) and a plurality of curved parts ( 12 ) which connect the straight parts; and a plurality of fins ( 20 ) coupled to the straight parts ( 11 ) respectively through a plurality of inner through holes ( 21 ), the refrigrant tube ( 10 ) has a joining portion of the curved parts ( 12 ) and the straight parts ( 11 ) coated with a metal layer ( 110 ).

TECHNICAL FIELD

The present invention relates to a fin tube type heat exchanger, andmore particularly, to a heat exchanger applied to a refrigerator forproducing cooled air supplied to a refrigerating chamber and a freezingchamber.

BACKGROUND ART

In general, other than the refrigerating chamber and the freezingchamber formed separated from each other, the refrigerator is providedwith a so called machine room in a lower part of the refrigerator, andair flow passages in rear parts of, and in communication with, therefrigerating chamber and the freezing chamber. The heat exchanger(evaporator) is fitted together with a blower in the air flow passage,for supplying cooled air to the refrigerating chamber and the, freezingchamber in association with a compressor and a condenser in the machineroom. That is, the high temperature, high pressure refrigerant suppliedthrough the compressor and the condenser is evaporated in theevaporator, and latent heat of the vaporization cools down environmentalair. The blower keeps circulating air throughout an inside of therefrigerator, to supply air cooled through the heat exchanger to therefrigerating chamber and the freezing chamber.

The foregoing related art heat exchanger for a refrigerator isillustrated in FIGS. 1 and 2;

Referring to FIGS. 1 and 2, the related art heat exchanger is providedwith a refrigerant tube 1 for refrigerant flow, and a plurality of fins1 fitted to the refrigerant tube 1 at fixed intervals in parallel withone another.

In more detail, in the heat exchanger, one line of the refrigerant tube1 forms one column, to which the fins 2 are fitted. FIG. 2 illustratestwo lines of refrigerant tubes 1 forming two columns.

Referring to FIG. 2, the fin 2, substantially in a small plate form, hasthrough holes 2 a for the refrigerant tube 1. That is, the related artheat exchanger has discrete fins 2 separable into individual pieces.Therefore, the fins 2 form discrete heat exchange surfaces along alength direction of the heat exchanger in a state the fins 2 are fittedto the refrigerant tube 1.

Moreover, a large amount of moist contained in air in the refrigeratoris frosted on surfaces of the heat exchanger due to an ambienttemperature, which is sub-zero, and interferes the air flow. Therefore,in general, a defroster 3 for melting the frost is provided to the heatexchanger, and a defrosting process is carried out during operationseparately, by using the defroster.

The heat exchanger is fitted in vertical position in the foregoing airflow path, such that the air in the refrigerator enters into the heatexchanger from below, and exits from top as shown in arrows after beingheat exchanged.

However, the foregoing related art heat exchanger has the followingproblems even if the heat exchanger is applied to most of refrigerators,currently.

For an example, the fins 2 are fitted to the refrigerant tube 1 one byone along the refrigerant tube 1 as the fins 2 are discrete andindividual. The fins 2 are arranged along the refrigerant tube 1 atintervals different from one another in an upper part and a lower partof the heat exchanger. That is, a flow resistance caused by growth ofthe frost deteriorates performance of the flow resistance, the fins 2are arranged at greater intervals in the lower part, the air entranceside where much frost is formed, than the upper part.

Moreover, the water formed by the defrosting remains at lower edges 2 bof each fins 2 as comparatively big water drops owing to surfacetension, and acts as nuclei of frost growth again in a followingrefrigerator operation (a cooling process). Therefore, as shown, it isrequired that the defroster 3 is in contact with all the lower edges 2 awithout exception.

At the end, the use of such discrete type fins leads a structure of therelated art heat exchanger complicate actually, and assembly of which isnot easy, too. Moreover, it is preferable that the heat exchanger forthe refrigerator has a small size and a high efficiency as the heatexchanger is located in a comparatively small air flow passage. However,due to the foregoing various problems, design change for optimization ofthe related art heat exchanger is not easy.

DISCLOSURE OF INVENTION

An object of the present invention, devised for solving the foregoingproblems, lies on providing a heat exchanger for a refrigerator, whichhas a simple structure and easy to fabricate.

Another object of the present invention is to provide a heat exchangerfor a refrigerator, which has an improved heat exchange performance.

Further object of the present invention is to provide a heat exchangerfor a refrigerator, which has reliability for a long time use.

To achieve the objects of the present invention, there is provided aheat exchanger for a refrigerator including a refrigerant tube having aplurality of straight parts and a plurality of curved parts eachconnecting the straight parts, and a plurality of fins for coupling withthe straight parts of the refrigerant tube through a plurality ofthrough holes therein, wherein the refrigerant tube includes coupledparts of the straight parts and the curved parts coated with a metallayer.

The metal layer is coated at least ends of the straight parts, andpreferably the whole curved parts and ends of the straight partscorrected to the curved parts. In more detail, the metal layer isextended by 15 min from the end of the straight part toward a center ofthe straight part.

The coupled part includes an expanded part at the end of the straightpart, an inserted part which is a part of the curved part inserted inthe expanded part of the straight part, and a metallic stuffing materialstuffed in a space between the expanded part and the inserted part.

Preferably, the expanded part has an inside diameter 1.3 times of aninitial inside diameter of the straight part, and more preferably, theexpanded part has an inside diameter 1.35-1.45 times of an initialinside diameter of the straight part.

Preferably, the expanded part has a length of minimum 3 mm, andpreferably a gap between an inside surface of the expanded part and theoutside surface of the inserted part is below 1 mm.

Preferably, the refrigerant tube is formed of aluminum, and the metal iszinc. Moreover, the refrigerant tube further includes a corrosionresistance layer coated on the metal layer.

In another aspect of the present invention, there is provided a methodfor fabricating a refrigerant tube of a heat exchanger for arefrigerator, including the steps of expanding ends of straight parts ofthe refrigerant tube such that each of the ends has an inside and anoutside diameters, inserting ends of curved parts in expanded ends ofthe straight parts, to pre-couple the straight parts and the curvedparts, and coupling the pre-coupled straight parts and the curved partsuch that a metal layer covers a coupled part of the straight parts andthe curved parts.

It is preferable that the method for fabricating a refrigerant tube of aheat exchanger for a refrigerator, further includes the steps ofcoupling the straight parts and fins in advance before the step ofexpanding ends of straight parts.

The ends of the curved parts are press fit to ends of the straight partspartially when the curved parts are inserted in the straight parts.

The coupling step includes the steps of dipping the pre-coupled curvedparts and straight parts in molten metal, and taking the dipped curvedpart and the straight parts out of molten metal.

The pre-coupled curved parts and the straight parts are dipped into themolten metal starting from the curved parts.

The coupling step may further include the step of pre-heating the curvedparts and the straight parts before the dipping step.

Preferably, the coupling step may further include the step ofpre-heating the curved parts and the straight parts before the dippingstep, or the coupling step may further include the step of applying ahigh frequency wave to the molten metal during the dipping step. Themethod for fabricating a refrigerant tube of a heat exchanger for arefrigerator, may further includes the steps of cooling down the coupledcurved parts and straight parts after the coupling step, and blowing airinto insides of the coupled straight parts and curved parts after thecoupling step.

The application of the straight fins facilitates simple structure andassembly process of the heat exchanger, and improves a heat exchangeperformance. Together with this, the use of aluminum refrigerant tubeand uniform welding of the coupled part facilitated by the dippingwelding permits a low production cost, an improved corrosion resistance,and a stronger bonding strength, and prevention of defects caused byleakage.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principles of theinvention:

In the drawings:

FIG. 1 illustrates a front view of a related art heat exchanger for arefrigerator;

FIG. 2 illustrates a section across a line I-I in FIG. 1;

FIG. 3A illustrates a front view of a heat exchanger for a refrigeratorin accordance with a preferred embodiment of the present invention;

FIG. 3B illustrates a section across a line II-II in FIG. 3A;

FIG. 4 illustrates a front view of a heat exchanger for a refrigeratorhaving a variation of refrigerant tube arrangement in accordance with apreferred embodiment of the present invention;

FIG. 4B illustrates a section across a line III-III in FIG. 4A;

FIG. 5 illustrates a graph showing a remained amount of defrosted waterper a unit fin area of the present invention and the related art;

FIG. 6 illustrates a graph showing a pressure loss vs. an operation timeperiod of the present invention and the related art;

FIG. 7 illustrates a flow chart showing the steps of a method forfabricating a refrigerant tube for a heat exchanger in accordance with apreferred embodiment of the present invention;

FIGS. 8A and 8B illustrate front views showing states of refrigeranttube in the steps of a method for fabricating a refrigerant tube for aheat exchanger in accordance with a preferred embodiment of the presentinvention;

FIG. 9 illustrates a partial enlarged view of a coupled part of arefrigerant tube fabricated according to a method for fabricating arefrigerant tube for a heat exchanger in accordance with a preferredembodiment of the present invention;

FIG. 10 illustrates a partial section of the coupling part in FIG. 9;and

FIG. 11 illustrates a section across a line IV-IV in FIG. 9.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which-are illustrated in the accompanyingdrawings. In explaining the embodiments, same parts will be given thesame names and reference symbols, and iterative explanations of whichwill be omitted.

FIG. 3A illustrates a front view of a heat exchanger for a refrigeratorin accordance with a preferred embodiment of the present invention, andFIG. 3B illustrates a section across a line II-II in FIG. 3A.

The heat exchanger of the present invention, on the whole, includes oneof more than one refrigerant tube 10 for forming a flow passage ofrefrigerant supplied from a condenser, and a plurality of fins 20 fittedto the refrigerant tube 10. The heat exchanger also includes one pair ofparallel reinforcing plates 30 fitted to opposite sides of the fittedfins 20.

The refrigerant tube 10 includes a plurality of straight parts 11 spacedat fixed intervals, and a plurality of curved parts 12 each forconnecting the straight parts 11. The refrigerant tubes 10, morespecifically, the straight part 11 are substantially arrangedperpendicular to direction of an air flow, and, as shown in FIG. 3B, oneline of refrigerant tube 10 forms one column in a length direction ofthe heat exchanger. In this instance, as shown in FIGS. 3A and 33B,straight parts 11 in different columns may be arranged in parallel toeach other in a horizontal direction. However, as shown in FIGS. 4A and4 b, for improvement of a performance of the heat exchanger, it ispreferable that the straight parts 11 are arranged alternately, togetherwith the through holes 21 in the fins. This alternate arrangementprevents bridging of frost grown between adjacent two refrigerant tubes10, thereby avoiding an increase of flow resistance.

Each of the fins 20 is a straight flat plate of a fixed length, having aplurality of through holes 21 forming one, or more than one column alonga length direction of the fin itself for coupling with the refrigeranttube 10. In more detail, the fins 20 are coupled with the straight partsof the refrigerant tubes 10 along lengths thereof at fixed intervals inparallel, extending to connect the straight parts 11 in the same columnin succession as shown in FIGS. 3B and 4B. Accordingly, water(hereafter, defrosted water) formed at the refrigerant tubes 10 and fins20 during the defrosting process is drained from the upper part to thelower part along the fins 10, smoothly. Moreover, the straight fin 20 ofthe present invention with a smaller number of lower edges than therelated art discrete fin, reduces an amount of the defrosted waterremained by surface tension.

This trend can be verified by an actual experiment. FIG. 5 illustrates agraph showing a remained amount of defrosted water per a unit fin areaof the present invention and the related art, where the discrete typefin (related art) and the straight fin (the present invention) arecompared, in which respective amounts of the remained defrosted waterare measured at a time after the defrosting process. As shown in FIG. 5,while 128.9 g/m² of defrosted water is remained in the case of thestraight fin, 183.8 g/m² of defrosted water is remained in the case ofthe discrete type fin, more than the straight fin. In more detail, theamount of remained defrosted water of the straight fin is no more than70% of the discrete type fin.

Moreover, the reduced amount of defrosted water is related to a pressureloss in the heat exchanger directly, which can be verified in FIG. 6showing variation of pressure loss vs. operation time period, clearly.Alike the experiment of FIG. 5, this experiment compares heat exchangershaving the discrete type fins and the straight fins applied theretorespectively, wherein the pressure loss is a pressure difference betweenan air entrance (the lower part of the heat exchanger) and an air exit(the upper part of the heat exchanger). In a first stage, variation ofthe pressure loss is measured during a dry heat exchanger carries outcooling for 60 minutes, and, in a second stage, variation of thepressure is measured during the heat exchanger carries out cooling for60 minutes, after a certain time period of defrosting in succession tothe first stage. Finally, in a third stage, variation of the pressure ismeasured during the heat exchanger carries out cooling for 120 minutes,after defrosting in succession to the second stage. As shown in FIG. 6,the pressure loss of the present invention is smaller than the relatedart in overall, and an increase ratio of the pressure loss expressed asa slope of the graph is also smaller. Actually, at ends of each of thestages, a pressure loss only approx. 42% of the related art is occurredin the present invention. This comes from a reduced flow resistancecaused by reduced frost and reduced frost increase ratio owing tosmaller amount of remained defrosted water. Along with this, the smalleramount of frosting allows smaller amount of heat transfer areareduction, resulting in no reduction of heat exchange rate.

Moreover, since the straight fin 20 of the present invention has aneffect of continuously arranged discrete fins, a smaller size heatexchanger of the present invention can provide the same heat transferarea with the heat exchanger of the related art. Also, the applicationof the straight fins 20 provides a simple structured heat exchanger, anda simple assembly process since the straight fin 20 can be coupled withthe straight parts of refrigerant tubes in the same column at a timeeasily.

At the end, the application of the straight fins 20 makes the heatexchanger of the present invention favorable in view of structure andperformance compared to the related art heat exchanger of the discretetype fins 20.

In the meantime, because the straight fins 20 are coupled with entirestraight parts of the refrigerant tubes 10 at a time, in general, therefrigerant tube 20 is fabricated by welding members formed separatelyinstead of fabricating as one continuous (unitary) member. That is,after certain members of the refrigerant tube 20 are coupled with thefin 20 at first, other members of the refrigerant tube 20 are welded tothe members coupled with the fin 20. In fabrication of the refrigeranttube 20, the refrigerant tube 20 is in general formed of aluminum, orcopper, and zinc is used as a welding material, mostly. The material isa factor that fixes a performance of the refrigerant tube 20, and thefollowing table shows properties of the materials. Thermal conductivityWeldability Price 1* Al Good Average Low Low Cu Very good Good High High1*: Risk of welding material (Zinc) corroded by potential difference.

As shown in the table, since there is not a great difference in thermalconductivities, aluminum is preferable as a material of the refrigeranttube 10, taking price into account. Moreover, because air in therefrigerator contains a large amount of moist, salt, and acids,aluminum, which has, not only a low risk of welding material corrosioncoming from potential difference, but also a high corrosion resistance,is further favorable compared to copper, except that the aluminum has aproblem of a lower weldability in fabricating the refrigerant tube 10 ofaluminum. That is, since aluminum is hardly fusible with other metal,application of a general welding method, in which a base metal is heatedto a temperature higher than a melting point of the base metal, toaluminum welding is not feasible. The present invention provides amethod for fabricating a refrigerant tube for supplementing the lowweldability of aluminum, which will be explained with reference to FIG.7.

FIG. 7 illustrates a flow chart showing the steps of a method forfabricating a refrigerant tube for a heat exchanger in accordance with apreferred embodiment of the present invention.

During fabrication of the refrigerant tube 20, ends of the straight part11 of the refrigerant tube 10 are expanded each to have an inside and anoutside diameters (S20).

As explained, the refrigerant tube 10 has a plurality of members formedseparately, i.e., the straight parts 11 and the curved parts 12,actually. Referring to FIGS. 8A-8b, for reducing a number of componentsof the refrigerant tube 10, it is preferable that only one side of thetwo sides of the curved parts 12 is formed separately, i.e., thestraight parts 11 are formed with the other side of the curved part 12as one unit. Therefore, in the expansion step (S20), ends of thestraight part 11 not connected to the curved part 12 are expanded, andthe curved part 12 formed separately is fitted to the expanded ends ofthe straight part 11.

In general, the ends may be expanded by inserting a tool therein, or byother methods. In order to prevent breakage of the ends, oil is suppliedto the end during the expansion continuously, and air is blown to aperiphery of the end for preventing entrance of other foreign mattersinto the straight part 11. For smooth infiltration of metal used as abonding material during the straight part/curved part bonding, the endof the straight part 11 is expanded to a diameter more than 1.3 times ofa diameter of an initial diameter. However, too much expansion may causebreakage of the end, it is more preferable that an inside diameter ofthe expanded end is limited to be 1.35-1.45 times of an initial insidediameter. The straight part 11 is expanded at least by 3 mm in a lengthdirection from the end, which facilitates smooth infiltration of themetal the same as the case of the inside diameter.

In the meantime, once the ends are expanded, coupling of the fins 20 andthe reinforcing plates 30 to the straight parts 11 becomes difficult.Therefore, before the expanding step (S20), it is preferable that thefins 20 and the reinforcing plates 30 are coupled to the straight partsformed as a unit with the curved part 12 (S20).

After the expanding step (S20) is finished, the straight parts 11 andthe curved parts 12 are pre-coupled (S30). In this instance, as shown inFIG. 8B, the worker inserts ends of the curved part 12 into the expandedends of the straight part. In this insertion, ends of the curved part 12are pressed into the expanded ends of the straight part 11, partly. Moreprecisely, the end of the curved part 12 is pressed into a part theexpanded end of the straight part 11 is reduced to an initial diameter.According to this, the curved part 12 is not separated from the straightpart 11 during final bonding.

After the pre-coupling step (S30), the straight part 11 and the curvedpart 12 are coupled completely by welding (S40).

In the coupling step (S40), the pre-coupled straight part 11 and thecurved part 12 are dipped into molten metal (S42). In the dipping (S42),the assembly of the refrigerant tubes 10, the fins 20, and thereinforcing plates are hung from a hanger such that the pre-coupledstraight part 11 and the curved parts face the molten metal, and dippedinto the molted metal starting from the pre-coupled curved part 12.Therefore, all the pre-coupled straight parts 11 and the curved parts 12can be dipped uniformly at a time. For adequate coating of the metal onthe whole curved part 12 and the end of the straight part 11, it ispreferable that the pre-coupled straight parts 11 and the curved parts12 are dipped into the molten metal to a depth 15 mm from the end of thestraight part 11.

The dipping step (S42) is carried out for 15 seconds, and it isappropriate that a temperature of the molten metal is approx. 400° C.The molten metal may be zinc, or other proper metal.

In the meantime, the curved parts 12 and the straight parts 11 may bepre-heated (S41) before the dipping step (S42). The pre-heating step(S41) is preferable since the metal is bonded to the curved parts 12 andthe straight parts 11 well, thereby improving weldability.

By the way, in the dipping step (S42), the straight part 11 and thecurved part 12 may be circled within the molten metal (S43). That is,the heat exchanger is slowly circled while the straight parts 11 and thecurved parts 12 are dipped in the molten metal, for better infiltrationof the metal between the straight parts 11 and the curved parts 12.

Moreover, a high frequency wave may be applied to the molten metalduring the dipping step (S42) for shaking the molten metal, andaccelerating the infiltration of the metal between the straight parts 11and the curved parts 12. Moreover, the high frequency wave makes thestraight parts 11 and the curved parts 12 to vibrate together, therebymaking the metal infiltration more active.

By taking the dipped curved parts 12 and the straight parts 11 out ofthe molten metal (S45) after the foregoing series of steps (S41-S44) arecarried out, the coupling step (S40) is finished. As a result of thedipping welding, exterior of the coupled straight parts 11 and thecurved parts 12 are covered with a layer of the metal.

After the coupling step, the coupled straight parts 11 and the curvedpart 12 are cooled for a time period (S50) by a fan or the like forquick solidification of the metal. Then, air is blown into the coupledstraight parts 11 and the curved parts 12, i.e., the refrigerant tube10, for checking blocking of the refrigerant tube 10 and dischargingforeign matters therein (S60).

As explained, because the dipping welding is applied to the method forfabricating a refrigerant tube of the present invention, the straightpart 11 and the curved part 12 can be coupled without being heated overmelting points. According to this, the refrigerant tube 10 can be formedof aluminum, resulting to drop of a production cost of the heatexchanger and improvement of corrosion resistance. It is understandableto a person skilled in this field of art that the method for fabricatinga refrigerant tube is applicable not only to a refrigerant tube ofaluminum, but also to a refrigerant tube of other material.

FIG. 9 illustrates a partial enlarged view of a coupled part of arefrigerant tube fabricated according to a method for fabricating arefrigerant tube in accordance with a preferred embodiment of thepresent invention, referring to which the form of the coupled part willbe explained in detail.

As shown, the refrigerant tube 10 of the present invention has thecoupled part coated with a metal layer on an outside of the refrigeranttube 10. That is, for coupling the metal layer 11, the straight part 11,and the curved part 12 from exterior, at least ends of the straightparts 11 are coated. Actually, the coupled part preferably includes thecurved part 12, the ends of the straight part 11, and a metal layer 110coated on the whole curved part 12, and the ends of the straight part11. A length ‘D’ of the metal layer 110 extended from the end of thestraight part 11 toward a center of the straight part 11 is 15 mm asexplained in the dipping step (S42).

Due to the expansion step (S20), the coupled part further includes anexpanded part 11 a formed at the end of the straight part 11 the curvedpart 12 is inserted therein before being coupled. Moreover, as shown inFIGS. 9 and 10, in view of interior, the coupled part further includesan inserted part 12 a, which is a part of the curved part 12 inserted inthe expanded part, i.e., the end of the straight part 11, and a metallicstuffing material 120 stuffed between the expanded part 11 a and theinserted part 12 a.

An inside diameter d₂ of the expanded part 11 a is 1.3 times of aninitial outside diameter d₁ of the straight part for smooth infiltrationof the stuffing material 120 between the expanded part 11 a and theinserted part 12 a. Actually,.for preventing breakage caused byexcessive expansion, it is favorable that an inside diameter d₂ of theexpanded part 11 a is limited to 1.35-1.45 times of the initial diameterd₁.

In the meantime, a ‘W’ is a gap between an inside surface of theexpanded part 11 a and an outside surface of the inserted part 12 a,which is actually one half of a difference of the inside diameter d₂,and the inside diameter d₁ as shown in FIG. 11. The gap W and the lengthL of the expanded part 12 a form a space for the metallic stuffingmaterial 120, and are an important factor of a bonding strength. Asexplained, the gap ‘W’ actually has a value below 1 mm, since anincrease of the inside diameter d2 of the expanded part 11 a is limitedto be within a certain range. Instead, the length L of the expanded part11 a is formed to be greater than 3 mm at the minimum, for providing anadequate bonding strength of the coupled part.

By the way, a general corrosion resistance layer is coated on all over asurface of the completed heat exchanger for preventing corrosion andspreading of the corrosion. Therefore, though not shown, the corrosionresistance layer is actually positioned on the metal layer 110 of therefrigerant tube 10, that may in general be a lacquer layer, or thelike.

At the end, as the coupled part is coupled both by the internal metallicstuffing material 120 and the external metallic material layer 110, acoupling strength is enhanced and defects caused by leakage is reducedin comparison to a general coupling method (actually, a welding method).Moreover, the metallic stuffing material 120 is formed more uniformly bycircling, or high frequency wave vibration, or the like during thecoupling process, thereby enhancing effects of prevention of defectscaused by leakage and strengthening a bonding force.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the heat exchanger for arefrigerator and method for fabricating a refrigerant tube of a heatexchanger for a refrigerator of the present invention without departingfrom the spirit or scope of the invention. Thus, it is intended that thepresent invention cover the modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalents.

Industrial Applicability

Basically, in the present invention, the application of continuousstraight fins improves defrosted water drain capability, and suppressesformation of the frost from the source. Therefore, the present inventionreduces a pressure loss (increased drain), improves a heat exchangeefficiency and heat exchange performance.

In comparison to the related art discontinuous discrete fins, the finsof the present invention have a simple structure, that permits an easyassembly of the heat exchanger. That is, the heat exchanger of thepresent invention has a reduced number of components in comparison tothe related art, and can dispense with separate forming and assemblyprocess, that reduces a production cost and improves productivity. Theapplication of straight fin permits reduction of a heat exchanger sizefor the same performance.

In the meantime, the application of the dipping welding in fabricationof the refrigerant tube permits to employ aluminum refrigerant tube,that permits reduction of production cost of the heat exchanger, andimprovement of a corrosion resistance. Moreover, since the refrigeranttube has a uniform and strong coupled part, the refrigerant tube becomesto have an increased coupling strength and a reduced leak defects, thatprovides a reliability for a long time period use, at the end.

1. A heat exchanger for a refrigerator comprising: a refrigerant tubehaving a plurality of straight parts and a plurality of curved partseach connecting the straight parts; and a plurality of fins for couplingwith the straight parts of the refrigerant tube through a plurality ofthrough holes therein, wherein the refrigerant tube includes coupledparts of the straight parts and the curved parts coated with a metallayer.
 2. A heat exchanger as claimed in claim 1, wherein the metallayer is coated including ends of the straight parts.
 3. A heatexchanger as claimed in claim 2, wherein the metal layer is coated onthe whole curved parts and ends of the straight parts connected to thecurved parts.
 4. A heat exchanger as claimed in claim 3, wherein themetal layer is extended by 15 mm from the end of the straight parttoward a center of the straight part.
 5. A heat exchanger as claimed inclaim 1, wherein the coupled part includes; an expanded part at the endof the straight part, an inserted part which is a part of the curvedpart inserted in the expanded part of the straight part, and a metallicstuffing material stuffed in a space between the expanded part and theinserted part.
 6. A heat exchanger as claimed in claim 5, wherein theexpanded part has an inside diameter 1.3 times of an initial insidediameter of the straight part.
 7. A heat exchanger as claimed in claim6, wherein the expanded part has an inside diameter 1.35-1.45 times ofan initial inside diameter of the straight part.
 8. A heat exchanger asclaimed in claim 5, wherein the expanded part has a length of minimum 3mm.
 9. A heat exchanger as claimed in claim 5, wherein a gap between aninside surface of the expanded part and the outside surface of theinserted part is below 1 mm.
 10. A heat exchanger as claimed in claim 1,wherein the fin has a form of straight plate extended along a lengthdirection of the heat exchanger.
 11. A heat exchanger as claimed inclaim 1, wherein the refrigerant tube is formed of aluminum.
 12. A heatexchanger as claimed in claim 1, wherein the metal is zinc.
 13. A heatexchanger as claimed in claim 1, wherein the refrigerant tube furtherincludes a corrosion resistance layer coated on the metal layer.
 14. Amethod for fabricating a refrigerant tube of a heat exchanger for arefrigerator, comprising the steps of: expanding ends of straight partsof the refrigerant tube such that each of the ends has an inside and anoutside diameters; inserting ends of curved parts in expanded ends ofthe straight parts, to pre-couple the straight parts and the curvedparts; and coupling the pre-coupled straight parts and the curved partsuch that a metal layer covers a coupled part of the straight parts andthe curved parts.
 15. A method as claimed in claim 14, furthercomprising the step of coupling the straight parts and fins in advancebefore the step of expanding ends of straight parts.
 16. A method asclaimed in claim 14, wherein the ends of the curved parts are press fitto ends of the straight parts partially when the curved parts areinserted in the straight parts.
 17. A method as claimed in claim 14,wherein the coupling step includes the steps of; dipping the pre-coupledcurved parts and straight parts in molten metal; and taking the dippedcurved part and the straight parts out of molten metal.
 18. A method asclaimed in claim 17, wherein the pre-coupled curved parts and thestraight parts are dipped into the molten metal starting from the curvedparts.
 19. A method as claimed in claim 17, wherein the coupling stepfurther includes the step of pre-heating the curved parts and thestraight parts before the dipping step.
 20. A method as claimed in claim17, wherein the coupling step further includes the step of pre-heatingthe curved parts and the straight parts before the dipping step.
 21. Amethod as claimed in claim 17, wherein the coupling step furtherincludes the step of applying a high frequency wave to the molten metalduring the dipping step.
 22. A method as claimed in claim 14, furthercomprising the step of cooling down the coupled curved parts andstraight parts after the coupling step.
 23. A method as claimed in claim14, further comprising the step of blowing air into insides of thecoupled straight parts and curved parts after the coupling step.
 24. Aheat exchanger for a refrigerator, the heat exchanger having arefrigerant tube having a plurality of straight parts and a plurality ofcurved parts each connecting the straight parts, and a plurality of finsfor coupling with the straight parts of the refrigerant tube through aplurality of through holes therein, wherein the refrigerant tubecomprising: an expanded part at each end of the straight part; aninserted part which is a part of the curved part inserted in theexpanded part of the straight part; a metallic stuffing material stuffedin a space between the expanded part and the inserted part; and a metallayer coated at least a part of surfaces of the expanded part and thecurved part.
 25. A heat exchanger as claimed in claim 24, wherein themetal layer is coated the whole curved part and the end of the straightpart coupled to the curved part.
 26. A heat exchanger as claimed inclaim 24, wherein the fin has a form of straight plate extended along alength direction of the heat exchanger.
 27. A heat exchanger as claimedin claim 24, wherein the refrigerant tube further includes a corrosionresistance layer coated on the metal layer.